The subject invention relates to surgical procedures and apparatus for the removal of bone. The subject invention is particularly directed to highly delicate procedures involved in areas such as brain and spinal surgery. The methods and apparatus according to the invention considerably reduce the risk of paralysis and other serious damage presently attendant to such procedures.
One procedure where the subject invention finds particular use is in the area of craniotomy flap removal, a procedure for opening up the skull used in brain surgery. The state of the art flap removal procedure involves use of a fluted drill to drill a series of "burr" holes in the cranium at spaced-apart locations around the section of cranium to be removed. A cutting tool is then inserted to join up the holes. Such a procedure may take from thirty to forty-five minutes and results in considerable loss of bone.
In the current approach to craniotomy flap removal, there is a considerable danger of penetration of the dura, a membrane lying between the brain and skull. There is also the risk of penetration of the brain itself. Such damage may result from the considerable plunging pressure which must be applied to drills currently in use and the tendency of such drills to "pull through" once they have penetrated completely through the skull.
In an attempt to reduce potential injury to the dura or brain, prior art drills have used a clutching mechanism to disengage the drill upon encountering soft tissue. However, at this point some damage may already have occurred, and the plunging pressure applied may still propel the drill into the subcranial matter.
Depth guages have also been suggested to indicate depth of penetration into the skull. However, such a device does not eliminate the plunging propensity of the drill. In addition, the varying thickness of the skull is an obstacle to accurate gauging of penetration. This variance may range from 0.080 to 0.30 inches thick.
Another highly delicate surgical procedure where the invention finds use is a procedure known as anterior surgical fusion. In this procedure, sections of bone must be removed from adjacent vertebra. Access to the vertebrae is gained by entry through the neck, which complicates the drilling approach. Slippage of the drill in such a procedure is an ever-present risk and has caused complete and permanent paralysis of patients. The present invention makes this process much safer by greatly reducing, if not entirely eliminating, the risk of accidental slippage or plunging.